1. Field of the Invention
The present invention relates to a golf club head. More specifically, the present invention relates to a wood-type golf club head with an adjustable sole contour.
2. Description of the Related Art
The prior art discloses golf clubs with means for adjusting the face angle. The face angle of a golf club is defined as the angle of the face to the grounded sole line with the shaft hole perpendicular to the line of flight. Maltby, Golf Club Design, Fitting, Alteration, & Repair, The Principles & Procedures, 4th Edition, Ralph Maltby Enterprises, (1995).
The perceived face angle is different than the measured face angle as would be measured on a device such as a CMM or De La Cruz gage. The measured face angle is based on the orientation of the face normal vector at a point in the center of the face. The perceived face angle is generally influenced by factors such as head outline shape at address and paint edge along the top of the face.
Alternative solutions to overcome the problem of variability of face angle at address include use of a dual keel point or multi-keel point sole shape, however these sole shapes have undesired affects on styling and on sound from striking the ball. Other inventions that allow for adjustments in the lie angle and face angle are also available. One such example is U.S. Pat. No. 7,281,985 for a Golf Club Head. The patent describes a golf club head which allows for the face angle, lie angle, loft angle, and shaft diameter of the golf club to be customized to a golfer. The customization of the face angle is accomplished by providing a golf club head with an insert for orientation of the golf club face angle following the manufacture of the golf club head.
A further example is U.S. Pat. No. 6,475,100 for a Golf Club Head With Adjustable Face Angle. The patent discloses a club head with an internal hosel and an insert disposed within that internal hosel. The insert allows for the face angle of the golf club to be oriented after manufacturing of the golf club head.
Yet a further example is U.S. Pat. No. 6,964,617 for a Golf Club Head With A Gasket. This patent discloses a golf club head with a gasket. The gasket controls the face angle of the club head. The width of the gasket varies to provide an open face angle club head, a closed face angle club head, or a neutral face angle club head.
Still another example is U.S. Pat. No. 7,377,862 for a Method For Fitting A Golf Club. The patent discloses a golf club head that has different hosel section orientations which allow for different face angles.
Woods, and in particular drivers, have historically been designed such that the sole shape (surface contour) is defined for styling or turf interaction purposes. Further, the center of gravity has been positioned in a location relative to the face in order to preferentially affect trajectory of the golf ball. The relationship between the sole shape and center of gravity of the golf club determines the face angle at address (natural sole) for a sole shape having a single contact point at equilibrium. This relationship has not been fully understood and as a result the face angle at address may often be different than intended in the design model. Some golfers are very sensitive to the look of an “open” or especially “closed” club face at address and this factor may weigh heavily in a purchase decision.
Whilst the club head design in CAD may orient the head in CAD space such that the face angle is at the desired value. This orientation is arbitrarily constrained and is not necessarily representative of the orientation when a player addresses the club and allows it to find an equilibrium orientation when resting on the ground.
Further, the resulting face angle at address may vary significantly with lie angle at address. This is because the area on the sole that touches the ground (“keel” area) is dependent on sole shape in proximity to the ground at a given lie angle. Different players are known to have lie angles at address for woods that are as much as twenty degrees different. Some wood heads may overcome this limitation by use of a dual keel point or multi-keel point sole shape. Sole shapes of this type often have undesired affects on styling and on sound from striking a ball.
Other wood clubs may overcome this by use of an adjustable shaft having a “kick” in the shaft axis relative to the bore axis of the head. This allows the face angle at address to be adjusted as desired within a range of several degrees open or closed by rotating the shaft about the bore axis. The disadvantage of this method is that the loft of the club head is simultaneously affected when rotating the shaft in this manner. Thus while a preferred face angle may be obtained by this method, the resulting loft may be too strong or weak.
As a driver is rotated thru a range of address lie angles the measured face angle will generally change by an amount related to the loft of the face at initial orientation and the range of lie angles rotated thru. For instance, a driver having a 10 deg loft and 0 deg face angle (also known as “Square”) at a design lie of 56 deg, will have a measured face angle that changes significantly (see FIG. 1) as address lie angle changes from 56 deg to 40 deg. This change in measured face angle is generally not perceived by the golfer as it doesn't result in rotation of the club head about a vertical axis. This behavior is widely considered desirable as it provides a consistent “looking” club at address for a wide range of players who may have different lie angles at address.